Spectroscopic line parameters of NH3 and PH3 in the far infrared

NH₃ and PH₃ rotation and rotation-inversion line parameters in the far to medium i.r. are calculated for remote sounding purposes of planetary atmospheres; 1607 lines of ¹⁴NH₃, 362 lines of ¹⁵NH₃ and 325 lines of PH₃ are compiled. The absolute intensity formulation has been reviewed in the case of rotation adn rotation-inversion lines of molecules with C_3v symmetry. The justification of the general agreement between the authors, and comparisons with other published expressions are given.     

Analysis of torsional splittings in the microwave spectra of dimethylether,CH3OCH3 and its isotopes,CD3OCH3 and CD3OCD3

The multiplet splitting patterns of microwave transitions in the ground state and the first two torsional excited states of CH₃OCH₃, CD₃OCD₃, and CD₃OCH₃ were analyzed in terms of the semirigid rotor models C_2vF-C_3vT-C_3vT and $\text{C}{}_3\text{F-}\text{C}{}_{\mathrm{3v}}\text{T-}\text{C}{}_{\mathrm{3v}}\text{T}\text{?}$. The following nonzero potential coefficients were obtained for CH₃OCH₃: V₃₀ = V₀₃ = 909.05 ± 0.49 cm^?1, V′₃₃ = 5.06 ± 1.60 cm^?1; for CD₃OCH₃: V₃₀(CD₃) = 897.18 ± 2.41 cm^?1, V₀₃(CH₃) = 910.45 ± 0.33 cm^?1; for CD₃OCD₃: V₃₀ = V₀₃ = 897.00 cm^?1. These results are compared to earlier microwave studies of these molecules.     

Rotational spectra of the deuterated carbon chain molecules: C3D, C4D, C3HD, and C4HD

The rotational spectra of the deuterated carbon chain molecules, C₃D, C₄D, C₃HD, and C₄HD, have been measured with the Fourier transform microwave (FTMW) spectrometer. The C₃D and C₄D radicals are produced by discharging the DCCD gas diluted in Ar. On the other hand, the gaseous mixture of HCCH, DCCD, and HCCD diluted in Ar is used for producing C₃HD and C₄HD. For C₃D, the molecular constants are determined from a joint least-squares analysis with the previously published millimeter- and submillimeter-wave data by considering the vibronic interaction between the ²Π ground state and the low-lying ²Σ vibronic state. The molecular constants of C₄D are determined by use of the conventional Hamiltonian of the ²Σ radical, while the effective rotational constant and centrifugal distortion constant are derived for C₃HD and C₄HD. In the present study, the hyperfine interaction constants of the deuterium nuclei in C₃D and C₄D are determined accurately. In particular, the nuclear quadrupole interaction constant, eQq, of the C₃D radical is found to be significantly smaller than those of C₂D and C₄D, indicating that C₃D has a floppy motion of the CCD bending mode due to the large Renner-Teller effect.     

Elastic constants of Cr3Si

Elastic constants of Cr₃Si have been measured on single crystals oriented along [110] and [100] as a function of temperature between 4.2 and 300 K. Their magnitudes at 4.2 K are in unit of 10¹¹ Nm^-2C₄₄ = 1.32C' = (C₁₁?C₁₂)/2 = 1.58B = 1.99 There is no peculiar behaviour as a function of temperature.     

Synthesis and characterization of a new monophosphate [2,5-(CH3)2C6H3NH3]H2PO4

Chemical preparation, calorimetric studies, crystal structure and spectroscopic investigations are given for a new noncentrosymmetric organic cation monophosphate [2,5-(CH₃)₂C₆H₃NH₃]H₂PO₄. This compound is orthorhombic P2₁2₁2₁ with the following unit-cell parameters: a=5.872(4), b=20.984(3), c=8.465(1) Å, Z=4, V=1043.0(5) Å³ and D_x=1.396 g cm⁻³. Crystal structure has been solved and refined to R=0.048 using 2526 independent reflections. Structure can be described as an inorganic layer parallel to (a,b) planes between which organic groups [2,5-(CH₃)₂C₆H₃NH₃]⁺ are located. Multiple hydrogen bonds connecting the different entities of compound thrust upon three-dimensional network a noncentrosymmetric configuration.     

Optical absorption spectrum and local symmetry of Tm ion in TmAl3(BO3)4 crystal

With the help of group theory analysis of absorption spectra of the transition ³H₆ → ³F₃ of Tm³⁺ ion in TmAl₃(BO₃)₄ crystal, measured at several temperatures from 1.8 till 293 K, it has been shown, that the local symmetry of the Tm³⁺ environment is C₃ and it decreases to C₁ at a low temperature. Effective selection rules and polarizations of lines at high enough temperatures (when the line-width is larger than the splitting in C₃ symmetry) have been obtained.     

Infrared electronic transitions of Eu+3 in GdAlO3

Infrared ⁷F_O → ⁷F_J electronic transitions are reported for Eu⁺³ in GdAlO₃. The low symmetry of the crystalline field allows the observation, for the first time, of transitions with J = 3, 4, 5 and 6. The spectra are explained by means of a crystal-field model where a C_s term is added as a perturbation to the cubic field in order to take into account the lattice distortion. This model predicts energy levels which are in good agreement with the experimental data.     

Room temperature magnetoresistance in Ln2/3A1/3MnO3 manganites

The investigation of the manganites La_2/3−xPr_xSr_1/3MnO₃, La_2/3Sr_1/3−xCa_xMnO₃ and La_2/3+xCa_1/3−2xAg_xMnO₃, which all exhibit Mn³⁺:Mn⁴⁺=2, shows that it is possible to reach high magnetoresistance at room temperature, up to 21% under 1.2 T. These materials are compared to La_5/6Ag_1/6MnO₃ which corresponds to the same Mn³⁺:Mn⁴⁺ ratio and exhibits a magnetoresistance of 25% in this field. An interesting feature deals with the value of the insulator-metal transition temperature T_IM, often higher than T_C, especially for Ag-based compounds. It is suggested that the latter results either from a better oxygenation of the surface of the grains or from a migration of silver toward the surface.     

The ν4 and ν2 Raman bands of CHD3

The CHD₃ Raman spectrum from 1925 to 2455 cm^?1 has been photographed with a resolution of about 0.2 cm^?1, showing the overlapping ν₂ and ν₄ bands. Ground state combination differences yield C₀ = 2.6297 ± 0.0003 cm^?1. The ν₄ state is weakly perturbed, but reasonably accurate values could be obtained for ν₄ = 2250.88 ± 0.10 cm^?1, (Cζ)₄ = 0.656 ± 0.010 cm^?1, C₄ - C₀ and B₄ - B₀. Some of these constants differ significantly from values previously estimated by infrared workers. For the ν₂ state the constants determined are in good agreement with recent infrared results.     

Laser Stark spectroscopy of the ν4 band of CH3C15N: Fermi resonance with 3ν83

Laser Stark spectra for the ν₄ band of CH₃C¹⁵N have been measured by using CO₂ and N₂O lasers. Almost 650 resonances have been assigned to about 140 ro-vibrational transitions with J′ ≤ 34 and K ≤ 11. An anomaly of the rotational structure around K = 7 has been proved to be due to a Fermi interaction by analyzing each K subband separately. Observed data have been fitted to a model which includes ν₄-3ν₈³ Fermi coupling by the method of least squares. The standard deviation of observed from calculated frequencies is 4.6 MHz. Molecular constants derived are also listed.     

Band analysis of the Swan system (d3Πg-a3Πu) of 13C2 and 12C13C molecules

The emission spectrum of the d³Π_g-a³Π_u system (Swan bands) due to ¹³C₂ and ¹²C¹³C molecules has been obtained in a low pressure hollow cathode discharge through a mixture of argon and benzene containing enriched ¹³C (90%). The spectrum was photographed on a 3.4-m Ebert spectrograph (reciprocal dispersion 0.54 Å mm^?1 in the first order). Isotope effect measurements have been carried out to determine the shift between isotopic bands and those emitted by ordinary molecules. The rotational analysis of six ¹³C₂ bands and three bands of ¹²C¹³C has been performed and molecular constants were derived.     

Lifetime measurement in the α system (C3Δ3-X3Δ3) of TiO

The radiative lifetimes of two rotational levels of the v′ = 2 level of the C³Δ₃ state of TiO have been measured using laser-induced fluorescence and delayed coincidence counting. Individual rotational levels are excited and observed. The measured lifetimes are τ_{J = 17} = 28.21 + 0.15 nsec and τ_{J = 87} = 29.74 ± 0.86 nsec. Argon-TiO collision cross sections have been determined for the two rotational levels and are found to differ by 30%.     

High-resolution laser spectroscopy of the Swan system (d3Πg-a3Πu) of C2 in an organic halide-alkali metal flame

The 0–1 band of the Swan system (d³Π_g-a³Π_u) of C₂ has been recorded by laser-induced fluorescence of C₂ formed by reaction between Na and C₂Cl₄. Most of the spectrum was recorded at Doppler-limited resolution, but overlapped lines were resolved using sub-Doppler techniques. The Q branches of the $\text{ΔΩ = 0}$ subbands and rotational lines for which $\text{ΔΩ = ±1}$ are observed for the first time. Molecular parameters defined in the effective Hamiltonian of Brown and Merer are obtained for both ³Π states.     

Theoretical Herman-Wallis coefficients for C70 and D70 and the dipole-moment function of HCl

Theoretical expressions for the Herman-Wallis coefficients C⁷₀ and D⁷₀ and a correction term of order 2B_e/ω_e times the leading term for C⁶₀ have been derived in terms of the Dunham potential-energy parameters and series dipole-moment expansion coefficients by the method of computer algebra. After reviewing previous work on the extraction of the dipole-moment function for HCl from experimental data, the present results are applied to a determination of the series representation up to seventh order in the reduced displacement from the equilibrium internuclear separation. Coefficients for an alternate representation in terms of a Padé approximant are also obtained; this model dipole-moment function should enable one to estimate more accurately the higher overtone and highly excited hot-band intensities since it circumvents the divergence difficulties of the series expansion and has the correct asymptotic behavior at both small and large internuclear separations.     

Emission and excitation spectra of Bi2Ge3O9:Eu3+

The emission and excitation spectra of the Bi₂Ge₃O₉:Eu crystal are observed at 77 K and 297 K. The spectra contain groups of sharp lines which are attributed to the transitions within 4f⁶ (Eu³⁺) configuration. The numbers of Stark splitting of terminal levels of transitions from ⁵D₀ and ⁷F₀ multiplets indicate that Eu³⁺ substitutes for Bi³⁺ in Bi₂Ge₃O₉. Tentative assignment of Stark levels of ⁷F_0-4 multiplets is made to crystal quantum numbers of C₃ symmetry which represents the site symmetry of Bi³⁺ in Bi₂Ge₃O₉. The following set of values of crystal field parameters of the C₃ point group is found to give the best overall agreement between the observed energy levels and the calculated levels: B²₀ = -533.84 cm^-1, B⁴₀ = 1085.99 cm^-1, Re(B⁴₃) = 327.57 cm^-1, Im(B⁴₃) = 75.209 cm^-1, B⁶₀ = 185.02 cm^-1, Re(B⁶₃) = - 68.475 cm^-1, Im(B⁶₃) = - 300.45 cm^-1, Re(B⁶₆) = 137.24 cm^-1 and Im(B⁶₆) = 882.29 cm^-1.     

Non-radiative energy transfer from Sm3+→Nd3+ in sodium borate glass

A study of energy transfer from optically excited Sm³⁺ to Nd³⁺ in borate glass has been performed. Contrary to the observations made by Cabezas and DeShazer, the Sm³⁺ → Nd³⁺ energy transfer has been observed as non-radiative. Energy transfer probabilities (P_da) and transfer efficiencies (η_T) have been calculated from our measurements of donor fluorescence intensity and decay times. The mechanism governing the transfer is electrostatic dipole-dipole in nature, contrary to the conclusions made by Nakazawa and Shionoya. At low acceptor (Nd³⁺) concentrations a linear dependence of P_da on acceptor concentration (C) has been observed which suggests the migration of excitation energy among donors. At high acceptor (Nd³⁺) concentration a plot of P_da vs (C_o + C)², where C_o is donor ion concentration, presents a linear dependence which is consistent with the Fong-Drestler theory of dipole-dipole energy transfer mechanism and interaction of one donor (Sm³⁺) with two acceptors (Nd³⁺).     

Carbon-13 Isotopic Species of H2C3, H2C4, and H2C5: High-Resolution Rotational Spectra

The microwave rotational spectra of the carbon-13 isotopic species of H₂C₃, H₂C₄, and H₂C₅ have been observed in a pulsed supersonic molecular beam by Fourier transform microwave spectroscopy. At high resolution all of the rotational lines exhibit hyperfine structure produced by the magnetic interaction between the nuclear spin of ¹³C and the overall rotation of the molecule. The component of the nuclear spin-rotation tensor along the a-inertial axis is large for most isotopic species, especially at the carbene carbon; at this position C_aa is two to three times larger than at other substituted positions along the chain. In contrast to both H₂C₃ and H₂C₃, in H₂C₄C_aa exhibits a pronounced alternation along the carbon chain backbone. Following detection of the five carbon-13 isotopic species and D₂C₅, an experimental structure (r₀) has been determined to high accuracy for H₂C₅.     

The electronic absorption spectra of [(CH3)3NH] MnCl3.2H2O single crystals

The electronic absorption spectra of [(CH₃)₃NH] MnCl₃.2H₂O single crystals are reported in the 15,000–45,000 cm^-1 region. In addition to the normally studied sextet → quartet transitions, special attention has been paid to the sextet → doublet transitions. Crystal field parameters evaluated (including the Trees' correction factor) to fit the observed spectra are B = 800, C = 2900, Dq = 680, and α = 76 cm^-1.     

Luminescence and energy transfer in Y2O3 CO-doped with Bi3+ and Eu3+

The emission spectra and decay times of the Y₂O₃ CO-doped with Bi³⁺ and Eu³⁺ have been investigated using site-selective excitation and time-resolved spectroscopy in the temperature range 8–296 K. Evidence for an energy transfer from Eu³⁺(S₆) to Eu³⁺(C₂) is given. The critical transfer distance R₀ = 8.6 Å was found from the decay curve.     

Analysis of the ν3, A-type band of C2H3D

The ν₃, A-type band of C₂H₃D centered at 1288.780 cm^?1 has been analyzed up to J = 33 and K_a = 15. The spectral range from 1351 to 1235 cm^?1 was recorded with a grill-spectrometer “type Girard” and with a resolution of 0.06 cm^?1, and a wavenumber precision of about 2 × 10^?3 cm^?1. From 787 identified transitions it was possible to calculate the rotational energies in the ν₃ excited state, and to refine the corresponding set of parameters.